1. Field of The Invention
This invention relates to attachment hardware for fastening adjoining concrete form panels together for assembling forms for poured concrete. More particularly, the present invention relates to a latching bolt system that permits the latching bolt to be removed easily even when it is subjected to substantial transverse shearing forces that bind it in the receiving aperture.
2. Related Art
Prefabricated concrete forms are frequently manufactured into panels having a face sheet 3 feet.times.8 feet (0.9 m.times.2.5 m). Many panels must be linked together to form a concrete form work for a structure of any significant size. Typically, panels and other forming members are butted together along the long dimension, or side of the panels, and fastened together by a fastening means such as a bolt and nut, a hinged latch or other means, or a wedge and bolt, with a form tie between two adjacent form panels. The form tie extends from one side of the concrete wall to the other to keep the opposed form panels from spreading apart when the concrete is poured.
An example of such a wedge and bolt assembly for joining panel units is disclosed in U.S. Pat. No. 4,194,717, issued to Easton et al. on Mar. 25, 1980; however, other such attachment hardware devices pre-existed the '717 patent.
Normally, a circumferential land or flange about the pin prevents the pin from penetrating the apertures too far. In some fastening systems the pin head includes a slot therethrough. A wedge may be driven into the slot to draw the pin fully into the apertures, wedging the wedge against one side rail and the flange against the other side rail of adjoining form panels with the form tie in between them to hold the pin firmly in place and prevent separation of the adjacent and adjoining panels. Typically, three or four such pins and form ties are employed to join two adjacent panels. The pin may be removably mounted on the rear side of the form panel by means of a mounting block that the pin slides through. The mounting block is typically bolted to the panel. The mounting block may be attached to a side rail or other portion of the rear side of the form panel by a base or mounting pad that is bolted to the form panel. The pin may have an overall length of about 12 inches (30 cm), with a pin head engaging portion comprising 21/2 inches (6.4 cm), of which the first 1/2 to 3/4 inches (1.3-1.9 cm) is tapered to assist in locating the pin in the holes during insertions. The remaining portion of the bolt is cylindrical, with the pin portion having a larger diameter than the bolt portion.
Such attachment hardware pins suffer from significant difficulties. As a first difficulty, it is exceedingly easy to misplace and/or damage the separate wedge pins required. Additionally, labor is used to connect the wedges to the pins. Further, when the form panels are aligned prior to pouring concrete, it may be relatively easy to align the holes or apertures in the side rails of the form panels and in the form ties and drive the pin into those holes by hammering on the back end of the bolt, but removing them can be extremely difficult.
The poured concrete, however, acts substantially like a fluid and develops significant hydrostatic head pressures throughout the concrete forms, which naturally become greater toward the bottom of the forms. The compressive loading on a concrete form 8 feet (2.5 m) high can easily reach 1,000-1,200 lbs. per square foot (420-506 kg/square meter). These forces may not be altogether evenly distributed. Moreover, the forces resisting them may not be evenly distributed throughout the concrete form panels, even among adjacent panels, as common bracing techniques on the rear of the panels may not be equally effective for adjacent panels. Consequently, the panels shift and spread somewhat relative to one another and relative to the opposed form panels, putting significant shear forces onto the pins of the attachment hardware.
Typically two spaced opposed parallel sets of forms are erected in order to pour a wall. Form ties are used to maintain the spacing between the opposed sets of forms. Typically the ties comprise strips of steel plate with one or more apertures toward each end. A plurality of ties link opposing form panels at each wall joint. The panel locking mechanism, such as a pin and a wedge, penetrates the side rail of one form panel, an aperture through the form tie, and a side rail of the adjacent form panel. These three elements are pulled together firmly by driving the wedge deeper into the pin slot. The hydrostatic forces generated by the poured concrete tend to spread the opposed form panels apart, but these outward or spreading forces are held in check by the form ties. In addition, the concrete expands as it sets, creating greater spreading forces. The pin is subject to a transverse pulling force by the form tie and an equal and opposed transverse outward pushing force by one or both adjacent form panels. Because the form tie is thin, these forces are quite close to each other, putting the pin into a significant bind. In a typical concrete wall, there may be about 7,000-8,000 lbs. (3,180-3,700 kg) tension or pulling force on each form tie. Because the only source of this force rises from counteracting the outward forces that otherwise would push the opposed form panels apart, the pin must be subject to equal outward forces, for a total transverse pin loading of about 14,000-16,000 lbs. (6,400-7,300 kg).
These forces tend to cause adjacent transverse cross sections of the pin to slip in opposite directions relative to one another, which defines a set of shearing forces on the pin. These shearing forces can make removing the pins very difficult, as the prior art pin has no way to relieve or release these shearing forces prior to removing the pin.
Consequently, removing the pins can be extremely difficult, often requiring an average of four to seven blows from a sturdy sledge hammer. The hammering can mushroom the pin point, causing interference with associated form tie apertures. In addition, the mushroomed pin points can easily shatter when struck with a hammer and may injure the worker. This requires much more additional labor than would be required if removal of the pins during disassembly of the form work were easy. In addition, the workers frequently damage or destroy the pins and significantly shorten the lives of the concrete form panel during disassembly of a form work.
In another problem, liquid from the poured concrete frequently splashes onto the rear sides of the forms. Sometimes significant amounts of concrete are spilled onto the rear side of the forms. Standard operating procedure calls for all the concrete form panels and associated hardware to be sprayed with light machine oil prior to usage so that concrete spilled onto them may be easily removed. Often, however, this step is omitted or the oil is rubbed off by the workers during the process of assembling the form. When concrete spills or splashes onto the attachment hardware it naturally sticks to the attachment hardware as it sets up and makes disengaging the latching pin much more difficult. It can also make it difficult to drive the bolt through the housing. Much of the abuse the attachment hardware is subjected to arises from chipping off the concrete that sets up on the attachment hardware.
Accordingly, there is a need for attachment hardware for concrete forming systems that is easy to engage between adjacent form panels; easy to remove after the concrete has set and consequently does not suffer the abuse of prior art attachment hardware leading to decreased labor costs and longer life for the attachment hardware; that substantially eliminates problems associated with spilled concrete adhering to the attachment hardware and setting up; and that allows the latching mechanism to be readily replaced with a similar mechanism or a different type of fastening mechanism.